fix(runtime): drain autoscaler example phases

[Coldwings]

Description

Make each autoscaler example load phase own and drain its submitted work before
the phase-local completion counter is released. This removes the queued-task
use-after-scope reported in #1022 and ensures the low-load phase starts only
after the high-load phases are empty.

The default workload now completes in a few seconds, while a dedicated
--smoke mode provides a short, timeout-bounded CI termination regression.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (optimization that improves speed/memory usage)
• Documentation (changes to documentation, comments, or examples)
• Refactoring (code changes that neither fix bugs nor add features)
• Tests (adding or modifying tests)
• Build/CI (changes to build system, CI configuration, or dependencies)

Related Issues

Closes #1022

Changes Made

Core Changes

• Retain one join_handle per submitted task and wait for frame destruction
  before a phase returns; the exceptional submission path drains already
  accepted tasks as well.
• Verify each phase reached its exact completion count and zero pending work
  before entering the next phase.
• Reduce the default task duration/count to a roughly four-second demo and add
  a sub-second --smoke profile.
• Run the smoke profile under a 15-second hard timeout in each Release CI
  matrix job.

API Changes

No library API or contract changes. The example adds the optional --smoke
command-line flag.

Testing

Unit Tests

• Added a process-level smoke regression for successful example termination
• Updated existing unit tests if needed
• Relevant checks pass locally

Integration Tests

• Built and ran the updated example out of source
• Ran the default autoscaling demonstration end to end

Sanitizer Testing

• Tested the example with ASAN and leak detection
• Tested with TSAN
• No ASAN or LeakSanitizer warnings or errors

Test Results

Release configure/build (TLS, HTTP, HTTP2, RDMA, TCP benchmarks disabled):
  cmake --build <release-build> --target autoscaler_example --parallel 2
  passed with developer warnings and warnings-as-errors

autoscaler_example --smoke:
  30/30 Release runs exited successfully within the 15-second CI timeout
  both phases reported Pending: 0 and their exact completion count before low load

autoscaler_example (default):
  exited 0 in 4.11 seconds
  demonstrated worker scaling from 2 to 8 and back to 2

ASAN_OPTIONS=detect_leaks=1:abort_on_error=1 autoscaler_example --smoke
ASAN_OPTIONS=detect_leaks=1:abort_on_error=1 autoscaler_example
  both exited successfully with no sanitizer diagnostics

CI workflow YAML parsed successfully.

Checklist

Code Quality

• My code follows the project code style
• I have added comments only where the lifetime constraint is non-obvious
• I have removed debug code and temporary instrumentation
• The changed example builds with warnings-as-errors

Documentation

• I updated the examples wiki and changelog
• The smoke invocation and phase-lifetime behavior are documented
• No API reference update is required

Testing

• The smoke regression proves successful process termination
• Default and smoke modes pass locally
• ASAN coverage passes locally; the repository CI will run its normal TSAN matrix

Compatibility

• The change is backward compatible
• No public library behavior changes
• CHANGELOG.md is updated

Performance

• The default example runtime remains practical and the CI profile is sub-second
• No benchmark is required for this example-lifetime fix

Reviewer Guidance

Areas requiring special attention:

• Verify that every exit after task admission waits for all retained task frames
  before the phase-local atomic is destroyed.
• Verify that the low-load phase cannot begin until both load phases report an
  exact completion count and zero pending tasks.
• Check that the smoke settings exercise queued work while remaining independent
  of exact timing or worker-count assertions on shared CI runners.

[Copilot]

Pull request overview

Fixes the autoscaler example’s queued-task lifetime issue by draining each load phase before releasing captured state.

Changes:

• Retains join handles and verifies each phase fully drains.
• Adds shorter default and --smoke workloads.
• Adds CI smoke coverage and updates documentation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
examples/autoscaler_example.cpp	Implements safe phase draining and smoke mode.
.github/workflows/ci.yml	Runs the smoke example with a timeout.
wiki/Examples.md	Documents phase lifetime and smoke usage.
CHANGELOG.md	Records the autoscaler example fix.

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